Frequency control method and frequency control apparatus

1. A frequency control method comprising: segmenting a range from a predetermined reference frequency to a predetermined lower limit frequency or a predetermined upper limit frequency into frequency range segments according to a number of battery apparatuses; detecting a current frequency of a power system; and causing battery apparatuses to charge from the power system or discharge to the power system in order to control a frequency or maintain a supply and demand balance of the power system, wherein the method causes lager number of battery apparatuses to charge or discharge as a frequency range segment including the current frequency becomes farther apart from the reference frequency.

2. The frequency control method according to claim 1 , wherein the frequency range segments include a first frequency range segment and a second frequency range segment, an absolute value of a difference between a frequency in the first frequency range segment and the reference frequency is equal to zero or higher to a frequency lower than a first value, and an absolute value of a difference between a frequency in the second frequency range segment and the reference frequency is equal to the first value or larger and lower than a second value, assigning first battery apparatuses that discharge or charge in all the frequency range segments, and second battery apparatuses that discharge or charge in the frequency range segments other than the first frequency range segment, according to at least one of a degree of degradation of, a remaining power quantity of, and a frequency of use of the battery apparatuses, and causing the first battery apparatuses to discharge to the power system and causing the second battery apparatuses not to discharge to the power system, or causing the first battery apparatuses to charge from the power system and causing the second battery apparatuses not to charge from the power system, when the current frequency of the power system is within the first frequency range segment.

3. The frequency control method according to claim 2 , wherein as a frequency deviation between the current frequency and the reference frequency becomes larger in each of the frequency range segments, causing the first battery apparatuses to discharge power more to the power system, or charge power more from the power system, and wherein in the first battery apparatuses, a rate of increase in the discharge power or the charge power with respect to the frequency deviation in the first frequency range segment is set higher than a rate of increase in the discharge power or the charge power with respect to the frequency deviation in any other frequency range segment.

4. The frequency control method according to claim 3 , wherein in the first frequency range segment, the discharge power from the first battery apparatuses to the power system increases from zero to first discharge power in accordance with the frequency deviation, and the charge power from the power system to the first battery apparatus increases from zero to first charge power in accordance with the frequency deviation, and wherein in the second frequency range segment, the discharge power from the first battery apparatuses to the power system increase from second discharge power lower than the first discharge power to third discharge power in accordance with the frequency deviation, and the charge power from the power system to the first battery apparatuses increase from second charge power lower than the first charge power to third charge power in accordance with the frequency deviation.

5. The frequency control method according to claim 3 , wherein each of the battery apparatuses comprises: a battery; and an inverter that discharges to the power system by converting direct-current power from the battery into alternating-current power, or charges the battery by converting alternating-current power from the power system into direct-current power, wherein as a capacity of the inverter in the first battery apparatus is smaller, a rate of increase in the discharge power or the charge power of the first battery apparatus in the first frequency range segment caused to be higher.

6. The frequency control method according to claim 3 , in the second frequency range segment, a rate of increase in the discharge power from the first battery apparatus to the power system is caused to match a rate of increase in the discharge power from the second battery apparatus to the power system, and a rate of increase in the charge power from the power system to the first battery apparatus is caused to match a rate of increase in charge power from the power system to the second battery power.

7. The frequency control method according to claim 4 , wherein each value of the first discharge power and the first charge power is a maximum rated value of the first battery apparatus.

8. The frequency control method according to claim 4 , wherein each of the battery apparatuses comprises: a battery; and an inverter that discharges to the power system by converting direct-current power from the battery into alternating-current power, or charges the battery by converting alternating-current power from the power system into direct-current power, wherein each value of the first charge power and the first discharge power is power that maximizes a conversion efficiency of the inverter in the first battery apparatus, or a charge and discharge efficiency of the battery, or a product of the conversion efficiency and the charge and discharge efficiency.

9. The frequency control method according to claim 7 , wherein the second discharge power is discharge power at a frequency resulting from subtracting the first value from the reference frequency in discharge characteristic data where the discharge power increases from zero at the reference frequency at a predetermined rate of increase to maximum discharge power of the first battery apparatus at the lower limit frequency, and wherein the second charge power is charge power at a frequency resulting from adding the first value to the reference frequency in charge characteristic data where the charge power increases from zero at the reference frequency at a predetermined rate of increase to maximum charge power of the first battery apparatus at the upper limit frequency.

10. The frequency control method according to claim 9 , further comprising: generating a correction command for each of the battery apparatuses in the frequency control apparatus, the correction command including a correction coefficient for each of the frequency range segments; transmitting to the battery apparatuses the correction commands respectively corresponding to the battery apparatuses from the frequency control apparatus; correcting a charge and discharge command value according to the frequency detected in the detecting in response to the correction command in each of the battery apparatuses; and discharging to the power system or charging each of the battery apparatuses from the power system in response to the corrected charge and discharge command value, wherein the charge and discharge value respectively represents charge power or discharge power uniquely set for the frequency in the charge characteristic data or the discharge characteristic data.

11. The frequency control method according to claim 9 , further comprising: generating a correction command for each of the battery apparatuses in the frequency control apparatus, the correction command including a correction coefficient for each of the frequency range segments; correcting a charge and discharge command value according to the frequency detected in the detecting on each of the battery apparatuses in response to the correction command; transmitting to the battery apparatuses the corrected charge and discharge command values respectively corresponding to the battery apparatuses from the frequency control apparatus; and discharging from each of the battery apparatuses or charging each of the battery apparatuses in response to the corrected charge and discharge command value transmitted from the frequency control apparatus, wherein the charge and discharge value respectively represents charge power or discharge power uniquely set for the frequency in the charge characteristic data or the discharge characteristic data.

12. A frequency control device comprising: one or more memories; and circuitry operative to: segment a range from a predetermined reference frequency to a predetermined lower limit frequency or a predetermined upper limit frequency into frequency range segments according to a number of battery apparatuses; detect a current frequency of a power system; and cause battery apparatuses to charge from the power system or discharge to the power system in order to control a frequency or maintain a supply and demand balance of the power system, wherein the device causes lager number of battery apparatuses to charge or discharge as a frequency range segment including the current frequency becomes farther apart from the reference frequency.